A power stage of a voltage step-up switch mode power supply (“SMPS”) drives the primary (low voltage) winding of a transformer with a high frequency alternating voltage, creating an alternating magnetic field around the primary winding and through a core of the transformer. One or more secondary (high voltage) windings are also wrapped around the core and are located in close proximity to the primary winding. The alternating magnetic field around the primary winding induces an AC voltage in the secondary winding. In most SMPS, the AC output of the transformer's secondary winding is rectified to provide a DC voltage at the output of the power supply. Compared with a low-frequency power supply, a high-frequency SMPS has a number of advantages, the most significant of which are suitability for low-cost manufacturing, and reduced size and weight. Consequently, SMPSs are considered to be more economical than low-frequency power supplies. With a voltage step-down SMPS the process occurs in reverse, with the primary winding being the high voltage winding and the secondary winding being the low voltage winding.
Surface mounted active and passive electronic components, commonly called surface mounted devices (“SMDs”), are typically employed in SMPS applications to further reduce the size and weight of the power supply. SMDs are also well-suited for automated and high-volume production, making them more cost-effective than non-surface mounted designs. In order to reduce the size of SMDs and thus further reduce the size and weight of the SMPS, it is necessary to increase the commutation frequency of the power devices in the power stage of the SMPS. When the commutation frequency is increased, the length of connecting wires conducting high frequency current between the power stage and the transformer are preferably minimized in order to eliminate parasitic impedances, which can reduce the efficiency of SMPS and generate electromagnetic interference (“EMI”). Parasitic impedances can be a significant issue with high-frequency SMPS where the high-frequency currents, e.g., typically in the range of about 100–200 kHz, often reach around 300 to 400 amperes in low-voltage circuits, e.g., in the range of about 10–60 volts RMS, of the SMPS. Losses and impedances in the connecting wires can be significant enough that it becomes unacceptably inefficient or impractical to use a high commutation frequency, thereby forcing SMPS designers to resort to lower frequencies, e.g., around 50 kHz, with the corresponding size and weight disadvantages.
There is a need for a cost-effective way to reduce parasitic impedances associated with connecting wires in high-frequency, high-current switch mode power supplies, this parameter being critical to good performance.